We are undertaking an analysis of the in vivo effects of a near-homogeneous T cell lymphokine with growth suppression and maturation induction activity for human leukemic cells. A near-homogeneous fraction (m.w. 50,000-65,000) was isolated from serum-free conditioned medium from PHA stimulated human lymphocytes (CM). We have shown previously that unseparated CM has maturation inducing activity for patient myelogenous leukemic cells in a liquid culture assay, and for mouse L1210 leukemia cells in vivo. The near-homogeneous CM fraction was shown to be enriched in activity compared to unseparated CM when tested with HL-60 human leukemic promyelocytes as the target cells. The activity of the near-homogeneous CM fraction will be tested using patinet myelogenous leukemia cells in vitro, and transplanted HL-60 tumors in nude mice. Liquid cultures of patient leukemic cells will be supplemented with amounts of the fraction having various units of maturation inducing activity. Cellular proliferation will be assayed by flow cytometry and autoradiography to determine the proportion of S phase cells, while induced maturation will be analysed by multiple differentiation markers. These include the development of membrane complement or IgG receptors, phagocytic capacity, lysozyme production, and reduction of intracellular RNA. The DNA content of immature and mature cells will be measured by flow cytometry to detect abnormal DNA stemlines, and establish the leukemic origin of the differentiated cells. For the in vivo experiment, various units of the near-homogenous fraction will be injected at the same time as, or after the implantation of HL-60 cells in nude mice. The resultant tumors will be analysed as to size, cell type, proportion of S phase cells, and tumorigencicity in subsequent transplantation. THe maturation inducer will be further purified to homogeneity in order to determin whether separate molecules are involved in growth suppression and maturation induction. The purified molecules will then be used as immunogens to preapare monoclonal antibodies for long-term studies of the regulation of hematopoiesis. The proposed research provides a direct approach to evaluate the effectiveness of an isolated T cell lymphokine forleukemic cell eradication, and its potential value as a therapeutic agent for the treatment of leukemia.